Tap



Patented Mar. 4, 1930 )UNITED STATES JOHN HUGO SMITH, OF DETROIT,MICHIGAN, ASSIGNOR TO THE WESSON vSALES COMPANY, OF DETROIT, MICHIGAN ACORPORATION F MICHIGAN TAP Applicationrle'd*February 15, 1926. SerialNo. 88,246.

This invention relates to taps for threading holes. It is'the Obj ect ofthe invention to provide a tap which will turn with less friction andput less strain on the material of which it I '5 is made, and thereforelast longer. This is on line 2 2 of Fig. 4 and through one set of landsof normal dimensions. Fig. 3 is a view similar to Fig. 2 but taken online 3-3 of Fig. 4 and through an alternate set of lands which arereduced in diameter.

Fig. 4 is an end elevation of the tap shown in Fig. 1 and illustratingvthe dierent diameters of the teeth inV the tap including the teeth' inthe working part, and the bottoming 1 partof the tap.

The shank has the usual land and intervening flut-es, but the radialprojection of the teeth on every other of theV lands, desig- .nated a,is cut down approximately 25% the depth of the teeth of the lands Z9.VThis is very well shown in comparing Figs. 2 and 3. However, I do notwant to be limited to any specific percentage of variation. The'angularity of the teeth in all the lands is preferably their same. Y

The only teeth in cutting the thread which Y simply pilot teeth whichguide andsteady the tool, and 'some of which may-.eventually becomeworking teeth when the tool is ground back inresharpening it.

I find by actual experience that by cutting off the crest 'oftheteethion someof the lands, that la great dea-l of thefriction in the.opera-V v tiony of the tool is eliminated, especially is thisA Y' truewith thelarge number Lof teeththat are really pilot teeth. The fact thatthese teeth do not reach to the bottom of the thread eliminates aconsiderablev amount of the fricwork are those at the end of thetap,-kno wn as y the start which are less than the teeth 1n the` fulldiameter of the tap. The other teeth are` y tion. Also it allows abetter distribution of the lubricant which can pass under each alternateland. This gives the lubricant double the time in' which to gatherbefore encounteringthe full depth tooth, and considerably betterlubricates all the pilot teeth. vThis,

therefore, provides two factors tending to lessen the resistance to theturning of the tool,

to wit: better lubrication', and less area of v surfaces in contact. y

Also, in theactual workingteeth of the tool I nd better results for thereason that alternate teeth cut only the sid-es of the thread,

while the other set of alternate teeth cut both the sidesand the depth.

The over all diameter of the teeth of each land is the same except theworking end of the tool where it gradually diminishes. However,the rootdiameter of all the teeth isthe same. The teeth on this portion of thetooll where the over all diameter of the teeth is not diminished arenotrelieved, as Awill be apparentfrom a comparison of Figs. '1 and 4.

, yThe root diameter being maintained uniform throughout it 'will' beobvious that the tool'inaybe ground back as it wears. The teeth notbeing relieved, it will'v be apparent vthese Yteeth may be readilysharpened by enp larging flutes kthrough grinding without'in any wayvarying the sizeof the thread which Y A bottoming can be produced Ybythetap Y WhatIclaim is; Y

tap for cutting threads, comprising ashank having a plurality oflongitudinally running. and circumferentially alternate lands fspacedlands and flutes, the ylandszprovided with' cutting teeth and the topsof the teethon .being partially removed, the "teeth forming each landbeing uniform'in root f `diameter and in over-all diameter, except at"the working .end where the root diameter is maintained but the lover-alldiameter gradually diminisl'ied;v the crest of eachv tooth'of uniformover-all' diameter being inthe form yof a segmentof a true circleand thecrest of each tooth *at the working end of -t-heitool being' relieved.

In testimony whereof I afIiXmy signature. y

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